Large-size manipulators find application, for example, with truck-mounted concrete pumps in which concrete is pumped by means of a concrete pump through a concrete-conveyance conduit that is carried on a multi-segment distribution boom, so that the concrete can be conveyed accurately and over a substantial distance to a particular target point. Conventionally the distribution boom consists of one or more segments and by means of appropriate hydraulic cylinders with deflection linkages can be folded at its articulated joints. The boom may be mounted either on a mobile undercarriage, generally a truck chassis, or a stationary platform and can be swivelled around a vertical axis.
In the case of conventional concrete pumps an operator steers the hose end of the conduit by means of a distant steering system towards the position where the concrete is to placed (rough positioning). This is done by means of direct operation of the valves associated with the individual cylinders of a hydraulic system. Another operator leads the terminal hose across the actual placing site (fine positioning). Depending on the particular design, elastic deformations will come into being in the segments of the distribution boom, so that the boom tends to set up vibrations. Particularly in view of the fact that conveyance of concrete by means of twin-cylinder thick-slurry pumps is pulsed rather than continuous, the distribution boom, and especially its last member, is induced to vibrate as the concrete issues from the terminal hose, so that a vibration amplitude of more than a meter may occur at the terminal hose. When the pumping frequency is in the region of the eigenfrequency (natural frequency) of the distribution boom, resonance vibrations may be set up. In conventional concrete pumps with distribution boom the concrete throughput of the pump and therefore the pumping frequency are throttled back sufficiently to keep the vibrations at the boom tip within limits, thereby avoiding danger for the operator guiding the terminal hose.